Fano antiresonances in x-ray-absorption spectroscopy

We calculate the x-ray-absorption spectra for a simple model for metals in which the attractive interaction between the core hole and a localized level produces a resonance in the conduction band. The model, a generalization of the Hamiltonian introduced by Kotani and Toyozawa, accounts for the electrostatic core-hole potential G acting on the conduction electrons. For G=0, a recently developed numerical technique that produces accurate results for the absorption rate over the entire x-ray frequency range shows, in agreement with the earlier analysis of the problem, that the spectra are affected by strong interference effects and display Fano antiresonances. The absorption rates are sensitive to the interaction between the conduction electrons and the core hole: For G{≠}0, the antiresonances are narrowed and displaced relative to the case G=0, and the spectra become remarkably dissimilar to either the initial or final densities of states.